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 close-up view of a CT scanner

What is a CT Scan?

  • CT scan machine A CT (computed tomography), also known as a CAT scan, uses many x-ray images from different angles and computer to produce cross sectional images.
  • This allows the radiologist (a physician specialized in radiology) to see inside the body. It is useful to view bone and soft tissues, which may not be well seen on a regular x-ray.

How does a CT Scan work?

  • The CT scanner looks like a large ring with a table attached to it. The table moves, allowing the CT technologist to position you inside the ring. The body part that that is being scanned will be inside the ring. The x-ray source is found inside the ring.
  • The x-rays are captured to show up as a picture on the computer monitor, usually in different shades of grey, although some scans are processed with colored images. A picture of your body is then created by the computer using the thin slices (cross-section).

What is a CT Scan Used for?

A radiologist can see bone, muscle, organs, brain tissue, blood vessels and nerves with a CT scan.

CT scan of a brain
three hospital employees observing a scan on a computer

How to prepare for your CT scan?

  • You may take your regular medication. Please bring a list of all your current medication.
  • If diabetic, take insulin as directed. You can have a light meal after taking insulin.
  • If you have allergies to any medication, food or other things, tell the staff before the test.
  • It is important to inform us if you have an allergy to iodine or to contrast agent, from previous CT or imaging exam.
  • If you are pregnant or think you might be, tell the staff before the test.
  • If you know or think that you will receive an IV contrast injection, for the 24 hour period leading up to the time of your CT exam, please drink a total of 8 glasses of water. You will be instructed to drink additional water after the exam. This will help flush the IV contrast out of your system.
  • You do not need a full bladder for this scan, so you can urinate before the exam. If you are on fluid restrictions, please contact the CT booking office for additional instructions.
  • CT Booking Office number is 613-761-4831, option 1.
  • During the weekday between 8 a.m. and 8 p.m.
  • For an abdomen and/or pelvis scan, you may need to spend up to 2 hours at the Hospital to drink oral contrast to highlight your bowel before the test.
  • Please inform us if you have an ostomy.
  • If you wish, you may bring a flavour enhancer (crystal light single servings, etc.) with you to add to your 2 oral contrast drinks to improve the flavour. Please no red coloured drinks.
  • If you are booked for a CT Enterography exam please be fasting 6 hours prior to your test.
  • As a general rule, please do not bring valuables to your appointment. You will need to remove any metal objects from your body, hair clips, glasses and removable dentures.
  • It is best to wear clothes without metal zippers or studs. In the event that you are wearing clothing that may interfere with the scan, you will be asked to change into a hospital gown.
  • You may take your regular medication. Please bring a list of all your current medications to show to the Technologist performing your scan.
  • Be prepared to remove any pumps or devices that should not be exposed to radiation ( i.e. insulin).

Safety Information

Breastfeeding and contrast agents

Mothers who are breast-feeding should be given the opportunity to make an informed decision as to whether to continue breast-feeding or temporarily abstain from breast- feeding after receiving IV contrast agent or gadolinium-based contrast agents. Less than 1% of the administered dose is excreted into breast milk and less than 1% of the contrast agent in breast milk ingested by an infant is absorbed from the gastrointestinal tract. Therefore, the expected dose of contrast agent absorbed by an infant from ingested breast milk is extremely low. Review of the literature suggests that it is safe for the mother and infant to continue breastfeeding after receiving such an agent.

If you remain concerned about any potential ill effects to your child, you may abstain from breastfeeding for 24 hours while continuing to express and discard the breast milk from both breasts during that period. In anticipation of this, you may wish to use a breast pump to collect milk before the contrast study to feed your child during the 24-hour period following the examination. Any further questions should be directed to your physician or the lactation consultant of TOH.

During the Exam

hospital employee smiling at the camera while sitting at a desk
a technologist manipulating a CT scanner
  • A technologist will ask you to lie down on a narrow table.
  • The technologist may ask to hold your breath at times to ensure a clear image.
  • The table will then slowly slide into the CT scanner. The scanner will look like the image shown.
  • A x ray tube will then move around in the scanner, to create detailed images.
  • You may hear clicking or whirring noises during the scan.

Can anybody be with me during the scan?

  • No, because the scan uses x-rays, other people should not be in the same room.
  • The technologist operates the scanner from behind a leaded glass window in a separate control room.
  • This protects them from repeated exposure to x-rays. They can observe you at all times through the window and you can speak with them through an intercom.
  • They are able to stop the scan at any time in case of emergencies.

Exam Information

Why oral contrast?

Oral contrast is used to better visualize the stomach, small bowel and large intestine. The amount of contrast and the length of time required to drink it is based on the specific reason for your CT scan. Some of the oral contrast has a bitter taste and you are welcome to add a flavour enhancer (Crystal light ® single servings etc.) to it. Some people may experience loose stools after some types of oral contrast.

It is important to inform us if you have an allergy to iodine or to contrast agent before you start your drinks.

What is intravascular (IV) contrast agent?

Intravascular contrast agent is an iodine containing solution. Because it shows up white on x-ray images, it is sometimes referred to as x-ray dye“. The doctor has requested and recommends a CT examination that requires injection of contrast agent either into your vein.

This injection will enable the radiologist (specialist doctor) to better see specific areas of your body (e.g. kidneys, brain, liver, arteries and veins. etc.).

There are two kinds of contrast agent used for injection into the bloodstream: non-ionic and ionic. These differ in how they react within the body. Non-ionic contrast agent is the safer of the two.

In Medical Imaging at The Ottawa Hospital we only use non-ionic contrast agent for your safety.

Is there any risk involved?

Mild allergic reactions, such as itching and hives, occur occasionally. These reactions may pass without treatment or respond quickly to medication. Very rarely, more severe allergic reactions can occur (0.045% of patients).

These can include a drop in blood pressure and irregularities of heartbeat. In extremely rare cases, stroke or death can occur (0.0005% of patients).

The doctors in charge of your case are aware of these risks and possible complications associated with the procedure that has been requested. In their opinion, the information to be gained about your condition outweighs these risks.

What should I expect?

  • You will be asked about your medical history and allergies.
  • If you have had a previous allergic reaction to contrast agent, it is very important that you let us know.
  • The technologist, nurse or doctor will do the injection of contrast agent.
  • Information specific to the contrast agent injection will be explained to you.
  • As the contrast agent is injected, you may experience a metallic taste in your mouth and a mild, warm sensation throughout your body.
  • These are normal reactions. In the rare event of an allergic reaction, as mentioned previously, the first 15 minutes after the injection are critical.
  • During this period, you will be watched very closely. Should you require any medical attention, trained staff and emergency equipment and drugs are immediately available and ready.

Post Exam Information

  • If you receive contrast agent you will be observed for 15 mins to observe any possible side effects following your procedure.
  • The needle will then be removed, you will be free to leave.
  • If no contrast agent was given you will be free to go immediately following the procedure.

Do I need to follow any special instructions after I go home?

  • The contrast agent is gradually removed from your blood by your kidneys and stored in your bladder until you urinate.
  • The colour of your urine will not change. You may immediately resume your normal diet. You are encouraged to drink several extra glasses of water within the next 24 hours to help your body remove the contrast agent.
  • Your injection site should be watched for swelling or bleeding. If it remains dry. You may remove the bandage or dressing after two hours, unless you have been otherwise instructed.

Call your referring doctor for advice if:

  • Significant swelling or bleeding occurs at the puncture site.
  • You experience any hives or itching.
  • You experience any difficulty in swallowing or breathing.
  • If you cannot get in touch with your own doctor, go to the closest emergency department.
  • It is also important to note that the iodine in the contrast agent can affect the results of some blood and urine tests.
  • If these tests are ordered within 48 hours of your x-ray procedure, please advise your doctor. If you have hyperthyroidism you may experience elevated TSH levels for one month or more after having an injection of contrast agent.

What Can I expect After the Scan?

You can return to your normal activities as soon as the scan is over. However, if your doctor had prescribed you to take a sedative to help with anxiety prior to your scan, you will need someone to accompany you home. You will not be able to drive until the effect of the sedative wears off.

You may ask the CT Technologist what the expected length of time will be for your report.

Exams Performed at TOH

What Type of CT Scans are Performed at The Ottawa Hospital?

Routine Scans​

  • Abdomen and Pelvis​​
  • Chest​​
  • Muscular Skeletal (Bones)​​
  • Head​​
  • Sinuses​​
  • Spine​​

CT Interventions

  • Biopsies​​
  • RFA​​
  • CT Angiography (CTA)​
  • Colonography (Bowel)​

CT Colonography (Bowel)

What is a CT colonography?

  • The CT colonography procedure consists of a CT scan of the abdomen/ pelvis after placing carbon dioxide or room air into your colon using a small rectal tube. The purpose of the air / gas is to distend the colon to eliminate any folds or wrinkles.
  • Most patients who have CT colonography, report a feeling of fullness when the colon is inflated during the exam, as if they need to pass gas. The feeling of fullness may continue for a few hours after the exam.
  • It is necessary to take pictures of your colon in two positions. Therefore, we will examine you lying on your stomach and on your back.
  • Occasionally a third set of pictures are required. You may also require an IV contrast injection as part of the procedure (x-ray dye that highlights the blood vessels).
  • Exam can take up to 2 hours or more (1.5hrs for the oral contrast and 30 or more minutes for the actual procedure).

What are the benefits versus risks?

Benefits

This minimally invasive test which provides 3D images that can depict many polyps and other lesions.

  • CT colonography is an excellent alternative or supplement to colonoscopy. It can be helpful for patients who have clinical factors that increase the risk of complications from colonoscopy.
  • CT colonography provides clearer and more detailed images than does a conventional barium enema x-ray.
  • CT colonography is tolerated well. Sedation and pain-relievers are not needed, so there is no recovery period.

Risks

  • There is a very small risk that inflating the colon with air could injure or perforate the bowel. This has been estimated to happen in fewer than one in 10,000 patients.
  • There is always a slight chance of cancer from excessive exposure to radiation. However, the benefit of an accurate diagnosis far outweighs the risk.
  • The effective radiation dose from this procedure is about 10 mSv, which is about the same as the average person receives from background radiation in 3 years.
  • Women should always inform their physician and CT technologist if there is any possibility that they are pregnant.
  • You can expect some level of pain/discomfort from this procedure.

CT Colonography PREP (Bowel)

Here’s how to prepare for your CT Colonography:

Proper bowel cleaning is needed for the best exam! If the bowel preparation is inadequate, we will not be able to do your exam.

To get a clean and empty colon you will start to prepare 1 (one) day before your exam. Purchase the Laxative and Barium Smoothie at one of the pharmacies listed at the end of this document. We recommend that you call ahead to ensure availability.

  • A clear liquid diet.
  • A laxative. The type of laxative depends on your medical condition. See prep 1 or prep 2. Please carefully follow the instructions.
  • Readi-Cat 2% barium smoothie.
  • Proper bowel cleaning is needed for the best exam! If the bowel preparation is inadequate, we will not be able to do your exam.

The Day before Your Procedure

Liquid Diet:

Starting at breakfast you may drink as many clear liquids as you want. Drink only clear liquids for breakfast, lunch, dinner, and snacks. Do not eat any solid foods. Drink plenty of fluid to avoid dehydration. Please avoid red liquids (i.e., red Jell-O or cranberry juice).

Clear liquids may include:

  • Water, tea, or coffee (sugar is okay, no cream or milk), Gatorade, Jell-O, Popsicles (no fruit or cream added, not red coloured),
  • Bouillon or broth, apple or white grape juice (no orange, tomato, grapefruit, cranberry or prune juice)
  • Soda such as Sprite, 7-Up, ginger ale, or cola
  • Lemonade (with no pulp)
  • Clear hard candy and gum are fine

IMPORTANT
It is extremely important that you drink at least 12 glasses of juice and/or water. If you do not drink a large amount of fluid, you will be at risk of dehydration and electrolyte imbalances.

Preparation 1

This preparation is for those individuals who do not have heart conditions, kidney disease, diabetes or a salt restricted diet. If you have any of these problems, use Preparation 2.

The laxative you should buy is called Pico-Salax (contains 2 packets).

DO NOT follow instructions on the box.

STEP 1: First Packet early morning, e.g. 8 a.m.

  • Empty the contents of one packet into a mug or cup.
  • Add 150 mL (5 oz) of cold water.
  • Stir to dissolve the laxative completely and drink.

STEP 2:

  • It is important to drink (250 mL/8 oz) of clear fluid every hour while the laxative is working.
  • You will need to be close to a toilet after you take this medicine as it can start working quickly.

STEP 3: Any time between 6 p.m. and 8 p.m.

  • Drink 250 mL of the Readi-Cat 2% barium smoothie.
  • Continue to drink water or clear liquids.

STEP 4: Second Packet 12 hours after Step 1 (e.g. 8 p.m.)

  • Repeat instructions as above for first packet.

Prep 1 Guide

 Day before your ExamDay of your Exam
BreakfastLiquid Diet + Step 1Liquid Diet
LunchLiquid Diet + Step 2 
DinnerLiquid Diet + Step 3 
EveningLiquid Diet + Step 4 

Preparation 2

This preparation is for those individuals with heart problems, kidney disease, diabetes or a salt restricted diet.

DO NOT use Pico-Salax if you have any of these problems.

STEP 1: 6 p.m.

  • The laxative you should buy is called Colyte.
  • Begin drinking Colyte at 6 p.m. as instructed. Drink a 250 mL (8 oz) glass every 10 minutes for about 3 hours. Rapid drinking of each glass is preferred instead of drinking small amounts continuously.

STEP 2: Between 6 p.m. and 8 p.m.

  • Drink 250 mL of the Readi-Cat 2% barium smoothie.
  • Drink at least 4 to 8 cups of clear liquids before and after.

Prep 2 Guide

 Day before your ExamDay of your Exam
BreakfastLiquid DietLiquid Diet
LunchLiquid Diet 
DinnerLiquid Diet + Step 1 
EveningLiquid Diet + Step 2 

Where to purchase the materials needed for the procedure

It is recommended that you call the pharmacy ahead to be sure that the materials are available.

Desjardins Pharmacy:The Ottawa Hospital Civic and General Campus
1053 Carling Avenue, Ottawa
OR
501 Smyth Road, Ottawa
613-761-4157
Shoppers Drug Mart:Central Ottawa – The Glebe,
700 Bank Street,
613-233-3202
 Ottawa West – Kanata – Signature Centre,
499 Terry Fox Drive
613-271-9790
 Ottawa East – Orleans – Fallingbrook Centre,
1675 Tenth Line Road,
613-837-607
 Ottawa South-West – Barrhaven – Chapman Mills,
3151 Strandherd Drive,
613-825-8717
 Carleton Place – Shoppers Centennial Pharmacy,
299 Lake Avenue East,
Carleton Place ON
613-257-4490
 Almonte Shoppers Drug Mart,
376 Ottawa St.
613-256-5238
 Winchester – Seaway Valley Pharmacy,
507 Main Street West,
Winchester ON
613-774-2633

The Day of Your Exam

Continue with your LIQUID diet

  • Medication: Take your regular medications. Please bring a list of your current medications to the appointment.
  • If you have diabetes, test your blood glucose level more often. Adjust your insulin or oral diabetes pills as discussed with your doctor. Resume your normal schedule after the exam. If your blood glucose level is low or you have symptoms, drink a clear liquid with sugar or take glucose tablets. Always recheck your blood sugar level to make sure it stays normal. We can still do the exam unless you need to eat solid food to maintain your blood glucose. It is better to maintain your blood glucose than to have the exam. We can always reschedule your procedure in the future.
  • If you haven’t been able to have a bowel movement or to finish the prep kit, please call us and we can reschedule the exam.

CT Preparation

Lung RFA (Radio Frequency Ablation)

Radiofrequency ablation (RFA)is a new way to treat lesions.

  • The RFA procedure is done under anesthesia and CT scan guidance.
  • CT is used to help guide the placement of the needle and the probe into the lesion.
  • The needle is used to take a biopsy specimen for pathological confirmation.
  • The probe (electrode) is then placed into the lesion and connected to a radiofrequency generator.
  • This results in heat generation and burning of the lesion.

After your procedure

  • When treatment is completed, the probe will be removed, and a small bandage will be placed over the insertion site.
  • The dead tissue will not be removed; the body will shed dead tissue through its natural functions. Ideally, over time, the treated tissue will shrink and be replaced by scar tissue.
  • After the procedure, you will be sent to a recovery area for approximately 1 to 4 hours.
  • You may feel some discomfort at the site after the procedure. Pain medication is available if you need it.
  • For patients who have no history of heart failure or kidney problems: Drink 8 to 10 cups of fluid per day for several days after RFA.
  • You may resume your usual diet.
  • Most patients will be on strict bed rest for 2 to 3 hours after the procedure.
  • Do no excessive physical activity for 24 hours, post procedure.
  • Do not drive a car, do not make any important decisions, and do not sign legal documents for 24 hours after the procedure.
  • The sedation you received may affect your judgment until it clears from your body.

Registration: Patient Information

  • You must present yourself 1 hour before your appointment time.
  • For the General Campus, please report to Diagnostic Imaging (Module X).
  • Bring your valid health card, and hospital green card with you.
  • Do NOT eat solid food or drink liquids after midnight the evening before your procedure.
  • You may drink water (2 cups ONLY) up to 3 hours before your arrival time to hospital.
  • Do not chew gum or suck on hard candy.

Medication

Take only the medications that you have been told to take by the doctor or nurse at your Pre-Admission visit. You may take them with a sip of water only. Please bring a list of your current medication.

You MUST bring these items with you to the hospital if you are prescribed any of the following:

  • Inhalers (for asthma)
  • Nitro spray (for chest pain)
  • Insulin (do not take the morning of surgery)
  • Pills for diabetes (do not take the morning of surgery)
  • If you have sleep apnea and use a machine at night, you must bring it with you on the day of surgery.
  • Do not wear perfume, scented lotions, aftershave, or use scented hair products. You may use deodorant unless told otherwise. (Perfume may cause severe allergic reactions for many people).
  • Remove all make-up, nail polish and all jewellery. Remove ALL body piercing jewellery.
  • Wear loose, comfortable clothing.
  • If you have any allergies to medicines, foods or other things, tell the staff before the test.
  • If you are pregnant or think you might be, tell the staff before the test.

You will need to have someone accompany you to the procedure.

  • All RFA’s are scheduled for a minimum of a one-hour period, but the procedure and recovery may take longer or shorter in duration.
  • If you are taking anticoagulants (blood thinners) such as Coumadin, Aspirin, ASA or other ASA containing medications, you should consult your physician to adjust your medications.
  • Ensure this is addressed by your physician a week prior to your procedure date.
  • The Physician will review the risks with you in more detail before the procedure begins.
  • You may ask questions at any time.

Bone RFA (Radio Frequency Ablation)

CT Guided RFA

  • Radiofrequency ablation (RFA) is a new way to treat Bone tumours/osteoid osteoma.
  • Osteoid Osteoma is a benign tumour of the bone that is most frequently found in the long bones, such as the tibia and fibula but can occur in any part of the body.
  • It usually affects young patients between the ages of 10-25 years.
  • The RFA procedure is done under anaesthesia and CT scan guidance.
  • CT is used to help guide the placement of the needle and the probe into the lesion.
  • The needle is used to take a biopsy specimen for pathological confirmation.
  • The probe (electrode) is then placed into the lesion and connected to a radiofrequency generator.
  • This results in heat generation and burning of the lesion.
  • The procedure requires a tiny incision but activity is typically not restricted following the procedure.

You will need to have someone accompany you for the procedure. All RFA’s are scheduled for a one-hour period, but the procedure may take longer or shorter in duration.

After your procedure:

  • When treatment is completed, the probe will be removed and a small bandage will be placed over the insertion site.
  • The dead tissue will not be removed; the body will shed dead tissue through its natural functions. Ideally, over time, the treated tissue will shrink and be replaced by scar tissue.
  • After the procedure, you will be sent to a recovery area for approximately 1 to 4 hours.
  • There is often some pain on the day of the procedure for which pain medication will be provided. However, within 24 – 72 hours most patients are able to tell that the typical tumour pain is gone. Most patients are pain free within 4 – 6 days.
  • For patients who have no history of heart failure or kidney problems: Drink 8 to 10 cups of fluid per day for several days after RFA.
  • You may resume your usual diet.
  • Do not drive a car, do not make any important decisions, and do not sign legal documents for 24 hours after the procedure.
  • The sedation you received may affect your judgment until it clears from your body. Make arrangements for a responsible adult to take you home after your procedure and stay with you overnight.
  • Your procedure may be cancelled if you do not have a responsible adult to take you home.
  • Patients may return to normal activities typically within the first week after the procedure. However, patients with lesions in the long bones of the leg are advised to avoid vigorous sporting activities such as long distance running, snowboarding or jumping for 3 months.
  • Your referring physician should have provided you with these details and follow up with them should be arranged within 2 weeks.

Preparation 1

This preparation is for those individuals who do not have heart conditions, kidney disease, diabetes or a salt restricted diet. If you have any of these problems, use Preparation 2.

The laxative you should buy is called Pico-Salax (contains 2 packets).

DO NOT follow instructions on the box.

STEP 1: First Packet early morning, e.g. 8 a.m.

  • Empty the contents of one packet into a mug or cup.
  • Add 150 mL (5 oz) of cold water.
  • Stir to dissolve the laxative completely and drink.

STEP 2:

  • It is important to drink (250 mL/8 oz) of clear fluid every hour while the laxative is working.
  • You will need to be close to a toilet after you take this medicine as it can start working quickly.

STEP 3: Any time between 6 p.m. and 8 p.m.

  • Drink 250 mL of the Readi-Cat 2% barium smoothie.
  • Continue to drink water or clear liquids.

STEP 4: Second Packet 12 hours after Step 1 (e.g. 8 p.m.)

  • Repeat instructions as above for first packet.

Prep 1 Guide

 Day before your ExamDay of your Exam
BreakfastLiquid Diet + Step 1Liquid Diet
LunchLiquid Diet + Step 2 
DinnerLiquid Diet + Step 3 
EveningLiquid Diet + Step 4 

Preparation 2

This preparation is for those individuals with heart problems, kidney disease, diabetes or a salt restricted diet.

DO NOT use Pico-Salax if you have any of these problems.

STEP 1: 6 p.m.

  • The laxative you should buy is called Colyte.
  • Begin drinking Colyte at 6 p.m. as instructed. Drink a 250 mL (8 oz) glass every 10 minutes for about 3 hours. Rapid drinking of each glass is preferred instead of drinking small amounts continuously.

STEP 2: Between 6 p.m. and 8 p.m.

  • Drink 250 mL of the Readi-Cat 2% barium smoothie.
  • Drink at least 4 to 8 cups of clear liquids before and after.

Prep 2 Guide

 Day before your ExamDay of your Exam
BreakfastLiquid DietLiquid Diet
LunchLiquid Diet 
DinnerLiquid Diet + Step 1 
EveningLiquid Diet + Step 2 

Last updated on: November 10th, 2023